This invention relates to a process for producing a polyolefin. More particularly, it relates to a process for polymerizing an olefin in the presence of a metallocene catalyst to produce a polyolefin in a stable manner over an extended period of time without suffering from adhesion of the product to the inner wall of the reactor or formation of a massive polymer.
Polyolefins exemplified by an ethylene polymer and a linear low-density polyethylene (L-LDPE), which is an ethylene-xcex1-olefin copolymer, are widely used as a film-forming material, an injection molding material, etc. These polyolefins have conventionally been produced by homo- or copolymerizing an olefin(s) by solution polymerization, suspension polymerization, bulk polymerization or gas phase polymerization in the presence of a so-called Ziegler catalyst system composed mainly of titanium, magnesium and a halogen.
Where production of a polyolefin particularly by gas phase polymerization, bulk polymerization or slurry polymerization is carried on for a long period of time, the product polymer tends to adhere to the wall or a stirring blade of a reactor. Cases are met with in which the adhered polymer melts to form a sheet-like polymer or a massive polymer that will clog the product discharge line and hinders the operation.
In order to avoid such operational trouble, it has been proposed to add an alcohol, a ketone, etc. (see JP-A-1-230607), water (see JP-B-7-5665) or a mixture of an alcohol phosphate and a quaternary ammonium salt (see JP-A-6-172412) to the reaction system, to charge water-containing particles (see JP-A-4-85307) or oxygen-containing particles (see JP-A-4-85308) into the reactor prior to the commencement of polymerization.
In addition to the Ziegler catalyst system, a catalyst system comprising a metallocene compound of the group 4 metal, such as zirconium or titanium has recently been developed (see JP-B-4-12283, etc.). The metallocene catalyst system has now been attracting attention, for the polymers obtained have such advantages that could not be observed with those obtained by using a conventional Ziegler catalyst. For example, the polymers obtained by using the metallocene catalyst have a reduced proportion of a low crystalline component, which is in favor of anti-blocking, and can have their processability controlled by introducing long-chain branches therein.
However, polyolefin production by gas phase polymerization, bulk polymerization or slurry polymerization in the presence of the metallocene catalyst cannot get rid of the above-described problems, i.e., adhesion of the product polymer to the reactor""s wall and a stirring blade and formation of a sheet-like polymer or a massive polymer. These obstacles to stable operation are common to the conventional Ziegler catalyst and the metallocene catalyst.
With respect to the metallocene catalyst, it is known that at least one compound selected from water, alcohols and ketones is added to the reaction system to improve the flowability of the polymer produced (see JP-A-7-76604). With this manipulation, however, operational hindrance due to formation of a sheet-like polymer or a massive polymer is still encountered frequently. Therefore, it has been demanded to develop a novel technique for achieving operational stabilization
The inventors of the present invention has found a method for realizing stable operation in producing a polyolefin using a transition metal-containing metallocene catalyst for an extended period of time which is not accompanied by formation of a sheet-like polymer or a massive polymer. The invention has thus been completed.
It is an object of the present invention to make it feasible to carry on stable operations for a long period of time in polymerizing an olefin in the presence of a transition metal-containing metallocene catalyst without involving adhesion of the produced polymer to the wall of a reactor or formation of a sheet-like polymer or a massive polymer.
The invention has been reached as a result of extensive study aiming at accomplishment of the above object. The invention provides a process for producing a polyolefin comprising polymerizing an olefin in the presence of [A] a transition metal-containing metallocene catalyst and [B] an organoaluminum compound represented by formula:
R1nAl(OR2)3xe2x88x92n
wherein R1 represents a C1-20 alkyl group, an aryl group, hydrogen, or halogen; R2 represents a C1-20 alkyl group, or an aryl group; and n represents a number of 0xe2x89xa6n less than 3, under such a condition that the temperature (Tw(xc2x0 C.)) of the wall of a polymerization reactor and the polymerization temperature (Tr(xc2x0 C.)) satisfy the relationship of the following formula 1: 0.5 less than Trxe2x88x92Tw less than 10.